1. Field of the Invention
The present invention relates to a scroll type fluid machine which is suitably used as an air compressor, a vacuum pump, or the like.
2. Description of the Related Art
In general, there has been known a scroll type compressor as a scroll type fluid machine in which an orbiting scroll is driven in an orbiting manner relative to a fixed scroll by means of a drive source such as an electric motor, whereby a fluid such as air is continuously compressed in a compression chamber provided between the both scrolls (for example, Japanese Patent Application Laid-Open Nos. 2000-74050 and 2001-82356).
Such a conventional scroll type compressor is constituted of a fixed scroll, an orbiting scroll opposed to the fixed scroll, and a rotation prevention mechanism. The fixed scroll is fixed to a casing and has a spiral wrap portion provided upright on an end plate. The orbiting scroll is provided in the casing in an orbiting manner and has a wrap portion provided upright on the end plate and overlapping with the wrap portion of the fixed scroll to define plural compression chambers. The rotation prevention mechanism is provided between the rear surface side of the orbiting scroll and the casing so as to prevent the rotation of the orbiting scroll.
In the prior art, an annular ball transfer race as the rotation prevention mechanism is provided so as to be opposed to the outer peripheral side of the orbiting scroll and the casing, and plural balls interpose between respective ball transfer races. According to this constitution, in the prior art, a thrust load acting on the orbiting scroll can be dispersed onto many balls, whereby a larger thrust load is supportable.
In the above prior art, a circular through-hole is provided in the ball transfer race, and the wall surface of the through-hole is curved, whereby the support of the thrust load on the orbiting scroll and the rotation prevention are simultaneously performed. However, when this constitution is applied to a large scroll type fluid machine with large inertia moment of the orbiting scroll, a force in a radial direction for stopping rotation force is insufficient, whereby the behavior in the rotational direction of the orbiting scroll becomes unstable.
In addition, in the prior art, the wall surface of the through-hole is curved, whereby the support of the thrust load on the orbiting scroll and the prevention of the rotation are simultaneously performed, and therefore, the curvature of the wall surface is required to be managed with high accuracy. In this respect, the prior art has such a configuration that, for instance, the ball transfer race is formed such as to surround an orbit bearing, and a large number of balls are arranged over the whole circumference of the ball transfer race. Therefore, the number of balls becomes extremely large, which causes increase in dispersion of dimension of the ball transfer race and that of the through-hole. As a result, the dimension management is difficult, whereby the manufacturing cost and the management cost tend to be increased.
Further, in the prior art, the rotation prevention mechanism includes balls and the ball transfer race arranged between the rear surface side of the orbiting scroll and the casing over the whole circumference. Here, the orbit bearing for rotatably supporting the orbiting scroll and a drive shaft is disposed on the inner peripheral side of the rotation prevention mechanism. In an oilless scroll type fluid machine, in order to supply a lubricant to each ball of the rotation prevention mechanism, the entire rotation prevention mechanism arranged in an annular manner is required to be sealed, and therefore, it becomes difficult to hold the lubricant.
The present invention has been made in view of the above problems, and it is an object of the present invention to provide a scroll type fluid machine which can realize the stabilization of the behavior in the rotational direction of an orbiting scroll, and, at the same time, the reduction in the manufacturing cost by the ease of the holding of a grease.